Welcome back; it’s been a while! We’ve been hard at work getting down to business with our Pikes Peak Airstrip Attack and the Pikes Peak International Hill Climb, both part of the Pikes Peak Speed Week. While we were running around losing our minds, SCR Performance was hard at work making great progress with the BRZ build. Last time, we covered what it takes to build a bottom end stout enough to handle our power demands. This week we’re diving into the cylinder heads to see how SCR improved the breathing capacity of the FA20/4U-GSE.

First off, engine efficiency was a key focus area in the stock design. Roller-rocker lifters were used to exploit the reduced friction between the camshafts and valves. Lighter valve springs were also employed so the engine didn’t have to work unnecessarily hard to open and close the valves.

Airflow into and out of the head was a strong consideration as well. The intake ports look generally large and the valve stems are fairly thin, both contributing to maximum air available to the combustion chamber. A potential choke-point is the exhaust port size that seems a bit on the small side, especially considering how much air we plan to stuff in there with 30 pounds of boost.

Lastly, the camshafts have nice, big, fat lobes so we probably won’t need to turn to an aftermarket set. With the use and progression of Variable Valve and Camshaft Timing, tuners are able to realize larger power gains through the manipulation of the base system versus relying on different camshaft designs that can sacrifice some real-world drivability.

Now, let’s take a look at what we did to improve upon the factory design and tailor to our soon to be boosted application!

FA20 / 4U-GSE VALVETRAIN

Picking up with the valve train, we knew we’d have to address the valve springs. While the stock valve springs are light, great for less resistance and overall efficiency of motor, they aren’t up to task if you're throwing 20 to 30 pounds of boost down the ports.

Our solution came with a valve springs kit from Kelford. The kit comes with stiffer, heavier springs so we can close the valves in the face of higher intake pressures thanks to the turbocharger. They also help to combat valve float at higher RPMs so we may be able to spin the motor a little higher to chase peak horsepower.

FA20 / 4U-GSE HARD-HEADED HARDWARE

With the increased pressure in the combustion chambers, we also wanted to make sure the heads would stay firmly attached to the block. For this we employed a Dynosty Head Stud Kit that features industry stalwart ARP hardware spec’d by Dynosty specifically for boosted FA20 applications.

To complete the seal between head and block and head and cam cover, we’re going with a brand new set of OEM gaskets. They check all of the boxes so SCR didn’t find a need to go aftermarket in this area.

As always, tolerances are critical to get right. For our application, we used the OE tolerance specs with some minor adjustments.

OK, we’ve covered the components that were changed, now on to the machine work performed in the head.

The goal of modifying the cylinder head is to increase the volumetric efficiency (VE). In short, this is how efficiently the engine can move the charge through the cylinders during the suck-squish-bang-blow process. The forced induction we plan to use helps to increase the VE (sometimes above 100 percent), but we also addressed a few other areas to smooth out the flow in and out of the cylinders.

WORKING THE HEADS OF THE FA20 / 4U-GSE

The first place to address is where the charge enters and exits the cylinder head: the intake and exhaust ports. The porting and polishing process not only increases the available area for air to flow through, it also smoothes out the passages to provide the most efficient flow. Additionally, you can shape the ports to best adapt to your desired powerband. You also want to make sure that you blend the ports into the bowl (area behind the valve) so you don’t hurt the velocity of the air while increasing the overall flow.

Through porting and polishing, we were able to increase flow on the intake side by 10 percent and a whopping 30 percent on the exhaust! That increase shows just how restrictive the exhaust side was and how it could inhibit the flow needed for a forced induction application. We need to get that exhaust out to help spin the turbine to get more air back into the engine!

In addition to the port and polish, we also had a multi-angle valve job performed. While it may not seem like there is much machining involved, this is one of the most important (and cost effective) modifications you can do inside the cylinder head. No matter how you slice it, all of the air must flow past the valves and, if they are of a less than aerodynamic shape, you’re going to interrupt airflow. Sharp angles, casting imperfections and an inefficient profile can all be negative attributes.

This process adds in additional cuts along the valve where it meets the head to reduce turbulence of the air flowing in. In ascending complexity and performance return (and cost), you have 3-angle, 5-angle and radius (5-angle with additional smoothing) valve jobs. Most street applications won’t need more than a 3-angle job as it provides the best compromise between cost and performance.

Finally, though not really for any performance gain, SCR machined the head where it mates against the head gasket. This is a best practice anytime that you pull a cylinder head off the block and you want to ensure the best seal possible.

The suspense is killing us, but we get closer and closer to a final product every week. Now that we’ve addressed the breathing issues within the head and how to keep the valves from head butting the pistons, we next turn our attention to the cooling, lubrication and fuel systems. This could be one of the most important installments of the build because we will need improvements in all three areas due to the increased heat and thirst from going turbo on our build. Stay tuned!

But. . . we're not done. As you can guess, our build is progressing a little quicker than we can keep up with our fully documented build logs. Two weeks ago, we officially unveiled the #RevvProjectBRZ at the Revvolution.com Shift-S3ctor Pikes Peak Airstrip Attack. Since it's been out in the public, we wouldn't want to leave you without some teaser pics, would we?

The Subaru BRZ / Scion FR-S Platform Series Partners

Please take a moment to check out our partners, whom without, none of this would be possible:

ABOUT THE AUTHOR

Grew up around cars and racing, a passion fueled by my whole family. Participated in numerous track days with cars and motorcycles as well as covered the NASA East Coast Honda Challenge for Grassroots Motorsports. Now that I'm in Colorado I'm enamored with the Pikes Peak International Hill Climb... borderline obsessive...